In DC (Direct Current)-DC power converters, such as buck converters, information regarding the zero crossing of the coil current may be used as an indication for the detection of a relatively low load of the power converter. The control of the power converter may then transition from a pulse width modulation (PWM) control mode (with a pre-determined switching frequency or commutation cycle rate) to pulse frequency modulation (PFM) control mode (with a changing switching frequency), in order to reduce the switching losses of the power converter.
Multiphase DC-DC power converters may be used to increase the amount of electrical power which can be provided at the output of the power converter, and/or in order to reduce the ripple of the output current which is provided at the output of the power converter. Such multiphase power converters may comprise a plurality of parallel constituent power converters, which may be operated in a plurality of different phases. The constituent power converters may provide respective fractions of the total output current and/or the total output power of the multiphase power converter. In other words, the plurality of constituent output currents (also referred to as the phase currents) which are provided by the plurality of constituent power converters, respectively, typically add up to the total output current (also referred to as the load current) provided by the multiphase power converter.
Differences in the parameters of the constituent power converters (e.g. caused by variances of a manufacturing process) may lead to differences in the phase currents which are provided by the plurality of constituent power converters. In other words, the phase currents which are provided by the different constituent power converters may differ from one another. In yet other words, the multiphase power converter may exhibit phase current offsets. Such phase current offsets may lead to a situation where the transition from a PWMcontrol mode to a PFM control mode (i.e. where the detection of a low load condition) based on the zero crossing of the phase currents cannot be performed in a reliable manner. In particular, in the presence of phase current offsets, the control of the multiphase power converter based on the phase currents may lead to instability problems and/or to increased switching losses of the multiphase power converter.
The present document addresses the above mentioned technical issues. In particular, the present document addresses the technical problem of providing a control circuit and a corresponding control scheme for controlling a multiphase power converter at relatively low loads in a stable and energy efficient manner.